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DOUBLE PRECISION FUNCTION DTZT01( M, N, A, AF, LDA, TAU, WORK,
$ LWORK )
*
* -- LAPACK test routine (version 3.0) --
* Univ. of Tennessee, Univ. of California Berkeley, NAG Ltd.,
* Courant Institute, Argonne National Lab, and Rice University
* September 30, 1994
*
* .. Scalar Arguments ..
INTEGER LDA, LWORK, M, N
* ..
* .. Array Arguments ..
DOUBLE PRECISION A( LDA, * ), AF( LDA, * ), TAU( * ),
$ WORK( LWORK )
* ..
*
* Purpose
* =======
*
* DTZT01 returns
* || A - R*Q || / ( M * eps * ||A|| )
* for an upper trapezoidal A that was factored with DTZRQF.
*
* Arguments
* =========
*
* M (input) INTEGER
* The number of rows of the matrices A and AF.
*
* N (input) INTEGER
* The number of columns of the matrices A and AF.
*
* A (input) DOUBLE PRECISION array, dimension (LDA,N)
* The original upper trapezoidal M by N matrix A.
*
* AF (input) DOUBLE PRECISION array, dimension (LDA,N)
* The output of DTZRQF for input matrix A.
* The lower triangle is not referenced.
*
* LDA (input) INTEGER
* The leading dimension of the arrays A and AF.
*
* TAU (input) DOUBLE PRECISION array, dimension (M)
* Details of the Householder transformations as returned by
* DTZRQF.
*
* WORK (workspace) DOUBLE PRECISION array, dimension (LWORK)
*
* LWORK (input) INTEGER
* The length of the array WORK. LWORK >= m*n + m.
*
* =====================================================================
*
* .. Parameters ..
DOUBLE PRECISION ZERO, ONE
PARAMETER ( ZERO = 0.0D0, ONE = 1.0D0 )
* ..
* .. Local Scalars ..
INTEGER I, J
DOUBLE PRECISION NORMA
* ..
* .. Local Arrays ..
DOUBLE PRECISION RWORK( 1 )
* ..
* .. External Functions ..
DOUBLE PRECISION DLAMCH, DLANGE
EXTERNAL DLAMCH, DLANGE
* ..
* .. External Subroutines ..
EXTERNAL DAXPY, DLASET, DLATZM, XERBLA
* ..
* .. Intrinsic Functions ..
INTRINSIC DBLE, MAX
* ..
* .. Executable Statements ..
*
DTZT01 = ZERO
*
IF( LWORK.LT.M*N+M ) THEN
CALL XERBLA( 'DTZT01', 8 )
RETURN
END IF
*
* Quick return if possible
*
IF( M.LE.0 .OR. N.LE.0 )
$ RETURN
*
NORMA = DLANGE( 'One-norm', M, N, A, LDA, RWORK )
*
* Copy upper triangle R
*
CALL DLASET( 'Full', M, N, ZERO, ZERO, WORK, M )
DO 20 J = 1, M
DO 10 I = 1, J
WORK( ( J-1 )*M+I ) = AF( I, J )
10 CONTINUE
20 CONTINUE
*
* R = R * P(1) * ... *P(m)
*
DO 30 I = 1, M
CALL DLATZM( 'Right', I, N-M+1, AF( I, M+1 ), LDA, TAU( I ),
$ WORK( ( I-1 )*M+1 ), WORK( M*M+1 ), M,
$ WORK( M*N+1 ) )
30 CONTINUE
*
* R = R - A
*
DO 40 I = 1, N
CALL DAXPY( M, -ONE, A( 1, I ), 1, WORK( ( I-1 )*M+1 ), 1 )
40 CONTINUE
*
DTZT01 = DLANGE( 'One-norm', M, N, WORK, M, RWORK )
*
DTZT01 = DTZT01 / ( DLAMCH( 'Epsilon' )*DBLE( MAX( M, N ) ) )
IF( NORMA.NE.ZERO )
$ DTZT01 = DTZT01 / NORMA
*
RETURN
*
* End of DTZT01
*
END
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